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swansont

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Everything posted by swansont

  1. There is also length contraction for which one must account. A thinks that B's clock is running slow, and B thinks his own clock is fine. But B also sees the travel as being length contracted, which makes it all consistent. So the travel that takes 45 minutes (75% of an hour) in one frame is only 75% of the distance in the other frame.
  2. I had a link to Box2D (very similar) a month ago. (HA!) http://blogs.scienceforums.net/swansont/archives/22
  3. CaCl2 is a salt, so for each mole of the solid, you get a mole of Ca and 2 moles of Cl in solution. So for that, it's .54 moles of solute in 20g. Figure out what the dissolved products are for the others.
  4. http://www.scienceforums.net/forum/showthread.php?t=21543
  5. Two things will happen: freezing point depression and a endo- or exothermic reaction when the material dissolves. Freezing point depression is a colligative property. That is, it depends on the number of moles of solute. Remembering that salts disassociate into their constituent ions when they dissolve, which will yield the better result?
  6. The 0.2 m is another misdirection. As long as it's less than a meter, the actual value doesn't matter. I interpret the 1 meter as the physical limit, not a work value: it's a dead-lift — that's how far you can lift using your legs. Any higher and you have to use your arm muscles, which tend to be weaker.
  7. or, to quantify that, a = GM/r^2 mass grows with r^3 if you have the same density. a should be 5^(2/3) = ~3 times larger , so one can conclude a slightly smaller density than earth.
  8. If there is a wave in the chocolate, you can't have the peaks and troughs in the same place if you reduce the speed, since the wavelength also changes. I don't think light traveling through the chocolate is the right way to analyze this. You have a field from a standing wave penetrate the chocolate and depositing its energy. There are a multitude of people who have done this experiment and documented it on the web. All the ones I've seen get close to 3e8 m/s. That's not consistent with measuring a wave in something with a significant change in index of refraction.
  9. Still, the force on wire A is due to the field emanating from wire B, present at wire A. Not at some point halfway in between, where the fields cancel. In reality, it would be due to the fields throughout the wire, which will have thickness and thus see a field gradient, and also depend on the current density distribution, but it's reasonably represented by an infinitely thin wire and the field at a point.
  10. It's not the physicists that generally cause the problem. Most people posting here with such questions aren't physicists. But the factor of gamma shows up in momentum, too, and in total energy, and I think that adds to the confusion.
  11. The rotation isn't about the CoM, so you needn't worry about that. All rotation is about A. What are the moments of inertia for all of the particles for rotation about A?
  12. No, I think the work is a misdirection, just as other data that are given, such as the dimensions, are. If you cannot exert a force larger than the weight, you will not lift the car.
  13. The question, though, is what is the length of the wave that is penetrating the chocolate. Is it the wavelength in the air, or the wavelength in the chocolate? Can a node in the air somehow become something other than a node in the chocolate? I think the key here is that you have a standing wave, not a traveling wave.
  14. The force is due to the field where the wire is, not at some other point.
  15. You'd have interactions that followed general relativity, and all of the relevant formulations of thermodynamic potentials. I'd imagine that writing them down would be exceedingly messy.
  16. No, I don't think that's it. The standing wave is in the air in the microwave, so the index of the chocolate isn't the problem. Others have recreated the experiment and gotten numbers reasonably close to c. And the density isn't the only factor in determining the index of refraction. Lightweight lenses for e.g. eyeglasses is a perfect example of lower density/higher index material.
  17. Unfortunately there are multiple definitions of mass, since there is the "relativistic mass" equation used by some. At least saying rest mass avoids some of the confusion.
  18. swansont

    Meter speed

    I'm not sure I understand the question. Your 60W lamp draws 60 W. Your 2.5 kW kettle draws almost 42 times as much power, so you are using electrical energy at a much faster rate. That's why your meter spins faster. Are you asking why the kettle draws more energy than the lamp?
  19. The Gossamer Condor and Gossamer Albatross http://en.wikipedia.org/wiki/Gossamer_Condor http://en.wikipedia.org/wiki/Gossamer_Albatross
  20. It's a little more subtle, though — AFAIK if you send in a pulse of coherent light (e.g. from a laser) you will get a coherent pulse out. So you've preserved the relative phase of the light. That's a little different than some other storage mechanisms that also rely on photon absorption. Atomic absorption and emission doesn't normally do this.
  21. To the extent that this is true, the time constant for it is long, not short. But the marketplace does have an influence.
  22. You run into trouble trying to explain quantum effects with a classical description, since there are going to be instances where the classical description fails, so forgive me if this sounds vague. The distance over which you have an electric field (that you might associate with the size of the photon) is not the same as the amplitude of the field strength. i.e. the graph that usually depicts the electromagnetic wave has axes of E and z, not x and z.
  23. No, it doesn't ignore that. The rebuilding is done in a more-or-less random fashion, and rezoning/rebuilding is a very site-specific endeavor. You'd have to seize property to do this (and there's precedent for doing so, but this would generally be much more valuable property). You're calling for "Big Dig" scale projects, and possibly larger, all over the place. All of this is in addition to the 1.6 trillion that the US needs to spend on infrastructure. And I'm leery of these utopian predictions (Bye bye traffic jams, etc) since they never seem to have panned out in the past. There are always the unforeseen complications.
  24. Units of time are not the same thing as time, just as units of distance (which are also man-made) are not the same thing as distance itself. Utter crap. Anything that operates in a predictable fashion can be used as a clock. Radioactive decay is used to measure time intervals all the time. Pulsars are used as clocks. Quartz oscillators are used in watches and many other clock systems. Sure there is. "Relative to the atomic time scale of the U.S. Naval Observatory, the flying clocks lost 59 ± 10 nanoseconds during the eastward trip and gained 273 ± 7 nanoseconds during the westward trip, where the errors are the corresponding standard deviations." That's from the abstract of the paper you obviously haven't read. You are in a very small minority.
  25. Time. Which is measured by counting the oscillations of an oscillator. (have I repeated this enough that you'll stop asking?) Have you read the paper? It's not assumed that just anyone can recreate the experiment. Someone with some training in the field, and with the proper equipment, could. (even an amateur like this guy) You misunderstand what is meant by observer. Anything that is present to experience the dilation counts anything that can make a measurement. The clock counts as an observer. Again, there's more detail in the paper — Wikipedia is not a substitute for that. It assumes some experience and basic level of competence in the field. Just like all journal articles do. Great care is taken in the building and operation of atomic clocks to assure that temperature, humidity, magnetic fields, vibration, etc. do not cause any effects.
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